Quantum Physics - Lesson 1.2 - Nuclear Radiation and Half Life

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Nuclear Radiation and Half Life Lesson 1.2 Electrons Nucleus The Nucleus is made up of protons and neutrons Nuclear Radiation is the emission of waves or particles from the nucleus of an atom Radiation is the emission of waves or particles from a source A model of the atom remember that a Proton has a positive charge and a neutron is neutral...

... but positive charges usually repel The Strong Vs The Electromagnetic Force The strong force is only dominant over very short distances electromagnetic electromagnetic strong strong electromagnetic strong electromagnetic Protons Stick! Protons Repel! So this works with smaller nuclei where the protons are all very close together, but what happens with larger nuclei? strong force easily dominant In larger nuclei, protons on opposite sides begin to experience electromagnetic repulsion This causes the nuclei to become unstable So how do these nuclei become stable ? ? ? Unstable nuclei will emit radiation in order to become stable. There are 3 types of radiation that they can emit: Alpha Radiation Alpha Radiation is the largest of the 3 types of nuclear radiation. It consists of 2 protons and 2 neutrons (a helium nucleus) which have broken off the original atoms nucleus. It is the most ionising form (dangerous) of nuclear radiationIt has the weakest penetration ability (it is the easiest to stop) Beta Radiation Beta radiation occurs when a proton turns into a neutron or a neutron turns into a proton. When this happens either an electron or positron (a positively charged electron) is emitted from the nucleus. Beta radiation has OK ionising ability and OK penetration ability. Gamma Radiation Gamma Radiation is really just excess energy from the nucleus being emitted in the form of high energy light.It is the most common form of nuclear radiation and is also the most penetrating. It has low ionising ability however as in order to ionise an atom, it must actually collide with it. So when does a radioactive nucleus emit radiation? It is actually impossible to determine exactly when an atom will emit radiation and decay. It is a bit like rolling a die and predicting when a 6 will be rolled, you can determine a probability of it occurring but that is all.

If you have many atoms however, you can predict how many will have decayed over any given amount of time.

This is known as Half Life Half Life The Half Life is the time taken for half of a radioactive sample to undergo radioactive decay.

Eg. If you have 20kg of Uranium 238 with a half life of approximately 4.5 billion years, you will have:10kg of Uranium 238 remaining after 4.5 billion years 5kg remaining after 9 billion years2.5kg remaining after 13.5 billion years1.25kg remaining after 18 billion yearsand so on. He 4 2 Helium Atomic Symbols Mass number (number of protons + number of neutrons) Atomic number (number of protons) Element Symbol Element Name Mnm 15 42 Emenemium